Large-size rolling bearings in the sense of the present patent application are to be understood as rolling bearings whose bearing rings are bolted through axially introduced passage and/or threaded bores with the connecting structures. Depending on their layout, large-size rolling bearings may be comprised of one or more ball or roller arrays. Appurtenant to each ball or roller array are two races which are finished by metal cutting in two to three bearing rings and subsequently hardened. Such bearing rings can be formed as nose rings, support rings, holder rings, disk-like axial rings, external rings or internal rings, etc.
The races of the bearing rings of large-size rolling bearings are hardened in feed operation with one or two inductors, applying a prior art method. According to this inductive feed hardening method, a so-called inductor, i.e. an induction coil or a pair of induction coils is provided for heating of the race, while for quenching a sprinkler fastened to the inductor and provided for feeding of cooling liquid is arranged above a zone of the race to be hardened which is small in relation to the ring diameter. During hardening, the inductor and the sprinkler once pass over the contour of the race of the entire ring in peripheral direction at a constant feedrate of the ring, so that each segment of the race is continuously heated and quenched.
With this prior art method, a small segment (slip), due to the process applied is incompletely heated. This small segment remains at the end point of hardening. In the area, the race remains softer.
Furthermore, according to the method described in DE 10228333 C1, the races of the bearing rings of large-size rolling bearings can be simultaneously heated with annular inductors by applying a full-surface recirculating heating process, which is also called shot-hardening, and subsequently be hardened by quenching. The benefit of this method lies in avoiding the soft spot described above.
Applying this method involves relatively high costs for the inductors as well as high generator performance rates. With very large rings, a uniform heating is problematic due to temperature-conditioned dilatation.